1.1. Technical Field
The present invention relates to flame retardant thermosetting epoxy molding compounds of the type comprising an epoxy, a hardener, a catalyst, a mold release agent, a filler, optionally a colorant, optionally a coupling agent and a flame retardant system. The flame retardant system comprises an oxidizing refractory metal oxide, particularly an oxidizing metal oxide of an element selected from Group VIA of the Periodic Table, and an organic compound containing halogen. The flame retardant thermosetting epoxy molding compound may be used, for example, to encapsulate a semiconductor device.
The present invention also relates to a method of encapsulating a semiconductor device by heat curing around a semiconductor device an encapsulating compound comprising an epoxy, a hardener, a catalyst, a mold release agent, a filler, optionally a colorant, optionally a coupling agent and a flame retardant system. The flame retardant system comprises an oxidizing refractory metal oxide, particularly an oxidizing metal oxide of an element selected from Group VIA of the Periodic Table, and an organic compound containing halogen.
The present invention also relates to an encapsulated semiconductor device wherein the encapsulant is the flame retardant thermosetting epoxy molding compound described above, the flame-retardant system comprising an oxizidizing refractory metal oxide, particularly an oxidizing metal oxide of an element selected from Group VIA of the Periodic Table, and an organic compound containing halogen.
A flame-retardant system comprising an organic compound containing a halogen and an oxidizing refractory metal oxide, particularly an oxidizing metal oxide of an element selected from Group VIA of the Periodic Table, was unexpectedly found to have flame retardant synergism when incorporated in thermosetting epoxy molding compounds used for encapsulating a semiconductor device.
The halogen-containing organic compound may be a separate ingredient, but is preferably a part of either the epoxy or the hardener. The halogen-containing organic compound can also be a halogen-containing compound which is chemically incorporated into the product of the epoxy resin and the hardener upon setting or part of other ingredients such as the lubricant or the colorant.
The flame retardant system may also comprise, optionally, antimony pentoxide and sodium. The flame retardant system may also comprise, optionally, basic magnesium oxide compound to reduce corrosion of metal conductor lines and pads of the semiconductor device.
The term "epoxy molding compounds" as used herein means epoxy molding compound conventionally known in the art including any material containing two or more reactive oxirane groups. For example, the epoxy molding compound may have two or more epoxy groups in one molecule, including glycidyl ether type such as, phenol novolac type; cresol novolac type and the like; glycidyl-ester type; alicyclic type; heterocyclic type and halogenated epoxy resins, etc. The epoxy resins may be used either singly or as a mixture of two or more resins.
Similarly, the term "hardener" as used herein means an epoxy novolac molding compound including, but not limited to, any phenol-derived and substituted phenol derived novolac hardener and anhydride hardener conventionally used as hardener for epoxy resins. For example, phenolic novolacs, and cresolic novolacs, are most suitable. The epoxy novolac molding compounds may be used either singly or as a mixture of two or more compounds.
The term "catalyst" as used herein means a catalyst appropriate to the hardener used to promote the curing of the present composition. Such catalysts include, but are not limited to, basic and acidic catalysts such as the metal halide Lewis acids, e.g., boron trifluoride, stannic chloride, zinc chloride and the like, metal carboxylate-salts such as stannous octoate and the like; and amines, e.g., triethylamine, imidazole derivatives and the like. The catalysts are used in conventional amounts such as from about 0.1 to 5.0% by weight of the combined weight of epoxy and hardener.
The term "mold release agents" as used herein means chemical agents commonly used to assist the release of the cured epoxy molding compounds from the mold. For example, carnauba wax; montanic acid ester wax; polyethylene wax; polytetrafluoroethylene wax; glyceral monostearate; metallic stearates; paraffin waxes and the like are suitable.
The term "fillers" as used herein means one or more of the conventional fillers such as silica, calcium carbonate, calcium silicate, aluminum oxide, glass fibers, clay, and the like. The preferred filler is silica or a mixture of predominantly silica with other filler(s). The fillers usually are used in at least 50 percent by weight of the molding compound.
The term "colorant" as used herein includes colorant commonly used in epoxy molding compound, such as carbon black, pigments, dyes and the like.
The term "coupling agent," as used herein means a coupling agent known to improve dry electrical properties of the compound. The coupling agents may be of the silane type, characterized by the formula R'Si(OR).sub.3 ; where R' represents an organo-functional group such as amino, mercapto, vinyl, epoxy or methacryloxy, and OR represents a hydrolyzable alkoxy group attached to the silicon. Preferred coupling agents are described in U.S. Pat Nos. 4,042,550 and 3,849,187, of which the descriptions are incorporated herein by reference.
The term "halogen-containing organic compound" or "organic compound containing halogen", as used herein, includes organic compound in which the halogen is present from any source including halogenation of a component or its precursor (such as a monomer) or by addition of halogen-containing monomers by reactions in which the halogen is not completely removed.
The halogen-containing organic compound used in a is preferably of the reactive type and further preferably has, as halogen, chlorine or bromine. Exemplary halogenated organic compounds are those types of polyglycidyl ether of bromophenolformaldehyde novolac, commercially sold by Nippon Kayaku under the tradename "BREN.TM.," those described in U.S. Pat. Nos. 4,042,550 and 4,282,136, of which the descriptions are incorporated herein by reference and include halogenated bisphenol A and derivatives of bisphenol A such as tetrabromobisphenol A, and glycidyl ethers of halogenated resins such as the diglycidyl ether of tetrabromobisphenol A.
Preferred is meta-brominated cresol epoxy novolac available from the Dow Chemical Co. under the tradename "Stable Bromine Cresol Epoxy Novolac" (71842.00L type or 71970.00 type, production no. R0544-91091-21-1. These are described in U.S. Pat. Nos. 4,727,119 and 4,731,423). The 71842.00L type is of the general formula: ##STR1## The 71970.00 type contains the following ingredients:
______________________________________ Diglycidylether of Dibromotetramethylbisphenol 0-8% Diglycidylether of Tribromotetramethylbisphenol 8-40% Cas No. 108935-90-6 Diglycidylether of Tetrabromotetramethylbisphenol 0-2% Cas No. 72436-58-9 Reaction product of cresol, formaldehyde & 60-90% epichlorohydrin Cas No. 064425-89-4 ______________________________________
The halogen containing organic compound may be a separate additive or may be contained in one or more of the organic components of the molding compound, especially the epoxy or the hardener, or possibly other components such as the lubricant, or the colorant or the filler (if organic).
Exemplary of reactive halogen-containing organic compounds which are part of the epoxy resin are metabrominated phenolics such as meta-brominated cresol epoxy novolac.
The term "oxidizing" means capable of at least partially oxidizing residual reduced sites on integrated circuit components where two different metals are in contact with each other, such as conductor lines, pads and ball-bonds. For example, for an integrated circuit having an Al.sub.2 O.sub.3 surface layer which passivates the metallic aluminum of the integrated circuit, oxidizing of the residual reduced sites thickens and strengthens the passivating surface layer.
The term "refractory metal oxide" means any oxide of any metal or alloy of any metal recognized as a refractory metal in the Manual of Classifiaction of Patents at page 75-1 of the December 1991 edition. These include titanium, zirconium, hafnium, vanadium, niobium, columbium, tantalum, chromium, molybdenum and tungsten.
The term "metal oxide of an element selected from Group VIA of the Periodic Table" means any Group VIA metal or alloy in any oxide form. Preferably, the metal oxide is tungsten or molybdenum. More preferably, the metal oxide is tungsten trioxide or molybdenum trioxide, both sold by Johnson Matthe Chemicals Ltd.
The term "antimony pentoxide" as used herein means antimony pentoxide in any available form. Preferably, antimony pentoxide used is Nyacol A1590 commercially sold by the Nyacol Division of P. Q. Corporation which has a sodium content of 0.03 to 0.06% by weight of the antimony pentoxide.
The term "magnesium oxide compound" as used herein means any magnesium oxide in any available form capable of neutralizing the acidity of the antimony pentoxide and thereby reducing the corrosion of the metal semiconductor device lines and pads, especially in regions where two different metals are in contact with each other. Preferably, the magnesium oxide compound is magnesium aluminum carbonate hydrate commercially sold by Kyowa Chemical Industry Co. under the trade name "DHT-4A".